1. Technical Field
The present invention relates to an image processing method, an image processing apparatus, a computer readable medium, and an imaging apparatus which perform blurring on part of local areas of an image.
2. Related Art
If a person is shot with a camera (imaging apparatus) with its shooting mode set to a portrait mode, the aperture of the stop is set wide and the depth of field is made shallow. A resulting image becomes such that the outline of the image of the subject person is clear whereas the background image is blurred, that is, the image of the subject person stands out sharply against the background image. Likewise, if a flower, for example, is shot with a camera in close proximity with the shooting mode set to a macro mode, an image can be taken in which the background portion is blurred and hence is not conspicuous while the image of the flower (main subject) is clear.
As described above, in shooting a subject with a camera in certain kinds of scenes, it is important to blur a background image. However, whereas a background image can be blurred easily in the case of a camera having a large-diameter lens, it is difficult to take an image with a blurred background in the case of a camera having a small lens such as a compact digital camera.
In the above circumstances, as exemplified by the conventional techniques disclosed in the following Patent documents JP-A-2008-271240, JP-A-2008-271241, and JP-A-7-021365, image processing has come to be performed so that blurring is performed on a portion to be blurred and extracted from a subject image.
An image having a superior touch of blur is obtained by performing blurring on a local portion (in the above example, background portion) other than a main subject portion of a subject image taken with a camera.
However, image quality improvement by blurring is attained only in a case that blurring is performed on an image taken with low ISO sensitivity (e.g., ISO 80 or ISO 100). If blurring is performed on an image taken with high ISO sensitivity (e.g., ISO 400, ISO 800, or higher), a problem arises that a main subject portion appears too rough and noisy against a background portion that has been subjected to the blurring, as a result of which the image loses unity and feels incongruous as a whole.